docs: def cone_meter_expansibility_Stewart(D, Dc, P1, P2, k):
      r'''Calculates the expansibility factor for a cone flow meter,
      based on the geometry of the cone meter, measured pressures of the orifice, 
      and the isentropic exponent of the fluid. Developed in [1]_, also shown
      in [2]_.
      
      .. math::
          \epsilon = 1 - (0.649 + 0.696\beta^4) \frac{\Delta P}{\kappa P_1}
  
      Parameters
      ----------
      D : float
          Upstream internal pipe diameter, [m]
      Dc : float
          Diameter of the largest end of the cone meter, [m]
      P1 : float
          Static pressure of fluid upstream of cone meter at the cross-section of
          the pressure tap, [Pa]
      P2 : float
          Static pressure of fluid at the end of the center of the cone pressure 
          tap, [Pa]
      k : float
          Isentropic exponent of fluid, [-]
  
      Returns
      -------
      expansibility : float
          Expansibility factor (1 for incompressible fluids, less than 1 for
          real fluids), [-]
  
      Notes
      -----
      This formula was determined for the range of P2/P1 >= 0.75; the only gas
      used to determine the formula is air.
  
      Examples
      --------
      >>> cone_meter_expansibility_Stewart(D=1, Dc=0.9, P1=1E6, P2=8.5E5, k=1.2)
      0.9157343
  
      References
      ----------
      .. [1] Stewart, D. G., M. Reader-Harris, and NEL Dr RJW Peters. "Derivation
         of an Expansibility Factor for the V-Cone Meter." In Flow Measurement 
         International Conference, Peebles, Scotland, UK, 2001.
      .. [2] ISO 5167-5:2016 - Measurement of Fluid Flow by Means of Pressure 
         Differential Devices Inserted in Circular Cross-Section Conduits Running
         Full -- Part 5: Cone meters.
      '''
      dP = P1 - P2
      beta = diameter_ratio_cone_meter(D, Dc)
      return 1.0 - (0.649 + 0.696*beta**4)*dP/(k*P1)